The present invention relates to a positioning mechanism for approaching a sharp probing tip towards a surface of a sample without damaging the probing tip, which probing tip is used as a sensor of a scanning probe microscope to measure a shape of surface and various physical quantities (electric potential, magnetism, friction, capacitance, and so on) of a sample, or used as a working needle of a micro-area processing machine for processing a sample surface by approaching the probing tip within several mm to several .ANG. from the sample surface.
The conventional SPM (Scanning Probe Microscope), as shown in FIG. 2, comprises two motion mechanisms in the vertical direction(z direction). Those are a coarse motion mechanism 6 and a fine motion mechanism 5. The coarse motion mechanism 6 is an approaching mechanism for approaching a probe 20 relatively within a distance of .ANG. order above a sample 3 after beginning to start moving from a position of several mm above the sample surface. The fine motion mechanism 5 is a controlling mechanism for controlling a distance between the probing tip and the sample surface at accuracy of .ANG. order to maintain constant a physical quantity such as an atomic force or a tunneling current occurring between the probe and the sample and thereby to measure a three-dimensional shape of the sample surface or various physical quantities (electric potential, magnetism, friction, capacitance, and so on) of the sample. For example, some of the coarse motion mechanisms comprise a pulse motor and a differential screw mechanism, and others comprise a pulse motor, a screw mechanism and a lever mechanism. The fine motion mechanism 5 usually comprises a Piezo element which drives the sample according to a supplied voltage. Therefore, since the conventional SPM needs a pulse motor and complex, precise screw and displacement reduction mechanism, and a Piezo element and a high voltage source for the Piezo element drive, it becomes an expensive structure. As there is a tradeoff between a moving range (dynamic range) of XYZ of the Piezo element and resolution, the whole Piezo element should be changed according to the measuring range. As the supplied voltage between electrodes of the Piezo element is very high, i.e. several hundred to a thousand voltage, it needs to shield a circumference of the Piezo element and to form a protection circuit for falling voltage when the cover of the device is opened. Especially at measurement of the sample in solution, current leakage between electrodes of the Piezo element easily causes a problem. As a supply voltage vs. displacement characteristics is nonlinear, another displacement sensor (for example, capacitance displacement sensor, strain gauge, and so on) is needed in order to measure accurate displacement (within 3% accuracy in the whole measuring range.)
It is desirable that a distance between the sample and the probe is more than several mm in case of changing the sample or the probe. When the probe is far from the surface of sample, the probe approaches at high speed, and when the probe approaches near the surface of sample, the speed is changed to low and the probe approaches the nearest position in order to approach measurement area in short time. For detecting the switching point from high speed to low, speed a long distance force acting between a sample and a probe (vibration amplitude of a cantilever attenuates by air resistance when the cantilever approaches the surface of sample) can be detected and change of speed can be carried out as shown in, or example, Japanese Opened Pat. H06-74745. A speed switching point can be determined by using the focal length of the objective lens of the optical microscope as shown in Japanese Opened Pat. H03-40355. In both Z coarse action systems, a motor and a screw, or a reduction system using a lever are used in the driving system. The moving distance for each one step is about 5 nm. Even at this distance, the last step is too long to control the distance between the surface of sample and the probe at accuracy of A level. In order to protect from contact of the sample and the probe, a sample table should be moved several nm. This is the distance which the Z coarse action drive system stops after making Z servo system including a Piezo element under the sample table active. At that time, the moving speed of the Z servo system must be higher than the rising time of one step of a motor. A detection of the end of Z coarse driving system is carried out by attenuation of vibrating amplitude or bend of a cantilever.
The present invention relates to Z coarse action and Z fine action of a scanning probe microscope. As the Z coarse action and the Z fine action are carried out by one driving device, the Z driving mechanism is simplified and the elements reduced as compared to the prior art mechanism. In Z coarse action, feed can be adjusted by stepless motion and the probe can approach the surface of the sample several mm to several .ANG. without damaging the probe. In Z fine action, the dynamic range can be varied by the switching mechanism.